Resistance-shunted lightining arrester



Aug. 19, 1941.

W. E. BERKEY ETAL RESI STANCE-'SHUNTED LIGHTNING ARRESTER Filed Sept. 26. 1939 f /I/ /l WITNESSES:

I INVENTORS Wii/mm L. Ber rey and Frecerak Joh 775072.

ATTORNEY &tentoi-Au 19, 1941 I "UNITED s''ATEs 'PATENTIIOFFICE- :.zsass ama I As cmoi September za, 1939, Serial No. 296.808

3Clalms.

our invention relates to exoess-voltage protective devices. and particularly, but not necessarily, to those which are utllized !or the protection of long transmission lines, or other lines or app ratus which are subject to excess-voltage surges of long duration. It is our belle! that mam iailures o! lightning arresters such as have been previously utilized have been directly the result of the !act that they have been called upon to discharge surges oi' long duration, or excess-voltage wave-forms which'talse a very abnormally long time to decrease ironi their maximum or crest value to the nermal voltage of thejarrester. such surges occur when a long transmission line is charged to an excessive voltagaand when that charge is eischargecl through a single arrester, without any substantial part of the surge-energy being clrained on- 'by other apparatus. such long discharges may also result from a lightning-shoke which itself is oi relatively long duration.

To dissipate gcess-voltage surges, a common type oi nrotective device has utilized a variableresistance, valve-type element which is capable of passing heavy discharge-current when impressed with voltages in excess oi! the rated voltage of the protective device, and which is capable oi substantially interrupting said discharge upon the return of rated voltage-conditions, said substantial interruption meaning a, reduction of the discha'ge-current either to a negligibly small amount, or to a somewhat larger value which m still considerably smaller than the maximum surge-current discharge-rate, and which is suffciently small so 'that the series gap-device, which is .norm ally connected in series with the valve-type element is capable oi' finally interrupting the discharge. A valve-type element of this nature has the property of changing rrom a relatively high resistance, which it has at the normal rated voltage of the device, to a relatively low resistance which it has under excess-voltage conditions when it'is discharging heavy currents; and when the applied voltage reduces again, and approaches toward the normal rated voltage of the device, the resistance of the element again returns substantially to its initial high value.

When such a variable-resistance. VaIVe-type element is utilized to dissipate a long-tall surge, or a surge requiring a long time to tall back to normal voltage-conditions after passing its crestvalue, the valve-type element begins to return to its high-resistance condition long, before the vates the'long-tail condition by materially slowing up the rate at which the tall-end ot the surge can be dissipated by the protective element. All of this means that the protective element is discharging for a very long time. being subjected to heating and other deleterious effects during this time. resulting in a very serious reduction in the life of the arrester, or its ability to handle repeated discharges, or even one discharge.

In accordance with our present invention, we I provide a relatively constant or non-variable resistance which is connected in parallel to a variable-resistance. valve-type element of the class.

'numher and severity of surges which can be withstood by a valve-type lightning arrester. particularly when subjected to surges of abnormal length or duration.

Tests have further shown that the addition of V our shunting resistor results ina material reduction in the voltage at which the arrester, with its series gap, breaks down, on fast-rising or steep-wave-ront, surges.

series gap oi a 73 kilovolt arrester may have a capacitance or, say, 10 micro-microiarads, passing a current of 10 ampe'es on a surge rising at 1000 kilovolts per microsecond. This occurs before the gap breaks down or arcs over. Under these conditions, an unshunted lightning-arrester block mayhave a resistance of something like 120 ohms per kilovolt, or approximately 9000 ohms i'or a 73 kilovolt arrester, giving a voltagedrop or. kv. at 10 amperes, which has to be added to the gap-breakdown voltage of about .110 kv. on such a wave-front, giving a total break-down voltage of 200 kv. With our shunting resistor of about ohms per kilovolt, this resistance-drop is reduced to 45 kv., giving a total break-down voltage oi' kv.

With the foregoing and other obiects in' view, our invention consists in the apparatus, structure, parts; combinations, systems and methods hereinatter described and claimed, and illustrated in the accompanying drawing, wherein:

On such surges, the v Figure 1 is a vertical longitudinal view through an arrester embodying ou` invention in a prei'rred form of embodiment, and

Fig. 2 is a similar view ot a modification.

In Figure 1, our invention is embodied in an arrester comprising a cylindrical porcelain housing 3 which houses the various`elements or the arrester. Starting at the bottom, it will be noted that the illustrated arrster comprises four arrester-blocks 4, surmounted by two so-called quench-gaps B which are in turn surmounted by two switching-gap structures I. the whole being held down, in firm contact with each other, by a spring 1 which is shunted by a fiexible Shunt 8.

Each one ot the arrester-blocks 4 comprises a central body-portion o which constitutes the variable-resistance, valve-type element, and which may be composed o! silicon-carbide granules or crystals and a binder. surrounding this valve-type core or element I 0, in the embodiment o! our -invention illustrated in Fig. 1, is a tubular resistance-member Il which, as, compared to the valve-type element lil, is of a relatlvely fixed resistance. being made of any of the well-known composition-materials which are utilized tor resistors, such as, a flnely subdivided reslstancematerial and a binder. Each oi' the blocks 4 ie coated, at each of its ends, with a terminal conductive coating |2 of sprayed copper or other good conducting material, preferably metallic. so as to make a good electric contact with the next element oi the stack of elements of which the arrester is composed.

In accordance with our invention, the resistor Il has a resistance which is less than 120 'ohms per kilovolt of the rated voltage oi the valve-type element across which it is shunted, or said resls tor should have a value which is oi' approximately 'the same order of magnitude as, or less than, that oi' the associated valve-type element in the final stages of the discharge, near the cut-oil' point oi the valve-type element.. We have successiully utilized resistors having a value lying in the range between 25 and 100 ohms per kllovolt of the rated voltage oi' the protective device, although we contemplate that even lower resistances can be utilized i! the series gap-devices are designed to interrupt the larger currents which would be drawn by any smaller resistance.

- The particular type of arrester-block I, as illustrated in Fig. 1, except for the specific range oi' resistance-values, is described and claimed in an earlier application, Serial No. 280,677, filed June 23, 1939 (case No. 20,444).

The series gap-device, which is connected in holes 22 therein.

series with the resistance-shunted valve-elements 4 in Fig. 1, is illustrated in a form in which it is divided into two parte. a so-called quench-gap part E and a so-called insulating orswitchlnggap-part i, as is fully described and claimed in a patent ot L. R Ludwig, W. G. Roman and ourselves, No. 2,135,085, granted November 1, 1938. The quench-gap device consists of a plurality of quench-gap elements Il preferably shunted by a resistor ll, so that this part of the gap-structure has the ability to reduce the final discharge-current to a value which can be handled by the switch-gar elements, which consists of a plurality of metalilc electrodes IS separated by insulators In operation, our arrester operates as any other valve-type arrester, except tor our addition of the resistor-elements H; When an excessive voltage occurs, the series-gap elements 5 and 6 nrst draw a certain charging-current. due to t eir v capacitance, and this charging-current produces a certain resistance-drop in the blocks 4. Because of our shunting resistors i l, this resistancedrop in the blocks is materially reduced. so that the ari-ester, as a whole, has a lower flashover or breakdown voltage on surges, particularly on steep-wave-front surges. As the surge-voltage continues to rise, the series-gap elements I and I finally flash over. applying substantially the !uli voltage of the excess-voltage surge to the re sistance-shunted valve-elements ID.

These valve elements thereupon change from their normal high-resistance condition to a lowresistance condition which permlts them to discharge heavy surge-currents, until the surgevoltage begins to return again so'as to approach the normal rated voltage of the protective devlce, at which tim the discharge-current oi' the valveelement falls sharply oi! to a small 'value which vares only relatively slightly as the voltage still further dccreases down towards the rated linevoltage of the device. Meanwhile, our Shuntconnected resistor. il is drawing a relatively constant current, which may have a Value oi the order of betweey. 10 and 40 ampercs, this value being perhaps something of the order oi' 1 or 2 times the :final discharge-current which is passed by the valve-element part ID when normal linevoltage is applied thereto. This final rcsistorcurrent of 10 to 40 amperes, plus whatever smaller current is being passed by the valve--type element ill at the time, is finally interrpted by the series gan-devices 5 and B, which thus imulate the arrester-blocks l from the line.

There are various ways in which a :relatively fixed resistance may be shunt-connected. in e!- i'cct, to a variable, valve-type resista'nce which constitutes the real lighting-arrester proper. The relatively fixed resistance can be molded in or With the arrester-block in various ways, or the resistor may be entirely separate. Furthermore, any suitable or convenient valve-type excessvoltage or lightning-arrester element may be utilized, not necessarily a block.

In Fig. 2, we illustrate our invention in the form o! a heavy-duty lightning-arrester which may comprise a main' insulatopbody 2! which has a plurality of vertically or longitudinally extending In one form of embodiment oi the invention, the insulator-body may be round in cross-section, and may have four holes 22 therein. In all but one of the holes 22, suitable valve-type lightning-arrestoielements 23 are placed, while the last hole contains an ordinary, relatively non-variable resistor-element 24. and it may also, but not necessarily, contain, at one end of the resistor-element, an auxiliary gapdevice 28 which is thus connected in series with the resistor-element, while the resistor and the auxlliary gap are together connected in shunt to all-oi' the lightning-arrester elements 23, which are in shunt with each other. The rcsistor 24 may conveniently be a composition-block ot molded resistance-materiai comprising a mixture of a finely divided resistance-material and a binder. The various elements which are disposed in the respective holes 22 are all connected in shunt with each other, and in series with the main series gap-device 21.

In operation, when an excesslve voltage is applied to the device shown in Fig 2, the main gap 21 first breaks down, as previously described, applying voltage to the various valve-type elements 23, causing the latter to dlscharge relatively heavy curre'nts, and at the same time, the voltage-drop across the valve-elements is applied to the resistor 24 with its serially connected auxiliary gap 25, causing the latter to break down and apply. to the resistor-element 24, suhstantially the arrester-voltage, minus the almost negligihly small arc-drop in the auxiliary grip-device. At the close of the discharge, the total -residual power-follow current passes' through the main gap 21, but most of this current is the current through the relatively fixed resistor 24, and the resistor-current also passes through the auxiliary gap 25. The auxiliary gap 25 serves, thereiore, as an auxiliary gap in series with the main gap 21. so far as the resistor-current is concerned, thus aiding the main gap in interrupting the relatively heavy power-follow current through the resistor-element 24.

While we have iliustrated our invention in two preferred forms of embodiment, we wish it to be understood that we are not limited to these particular forms, as many changes, in the way of substitutions, additions and omissions, may be made by those skilled in the art without departing from the essential spirit of our invention. We desire, therefore, that the appended claims shall be accorded the broadest construction consistent with their language and the prior art.

We claim as our invention:

1. An excess-voltage protective device comprising a variable-resistance valve-type element capable of passing heavy discharge-currents when impressed with voltages in excess of the rated voltage of the protective device, and of substantially interrupting said discharge upon the return of rated voltage-conditions, a resistor of relatively fixed resistance, means for connecting said resistor in shunt to said valve-type element, and a series gap-means in series circuit relation to both said valve-type element and said resistor, characterized by said resistor having a resistance less than 120 ohms per kilovolt of the rated voltage of the protective device, and said series gan-means being capable of interrupting the combined currents of both said valve-type elementand said resistor at the rated voltage of the .protective device. I

2. An excess-voltage protective device com prising a variable-resistance valve-type element capable of passing heavy discharge-currents when impressed with voltages in excess of the rated voltage of the proteetive device, and o! substantially interrupting said djscharge upon u the return of rated voltage-conditions, a resisterof relatively fixed. resistance, means for connecting said resistor in shunt to 'said valve-type element, and a series gap-meansin series circuit relation to both said valve-type element and said resistor, charaeterized by said resistor having a. resistance of approximately the same order of magnitude as, or less than, that of the Valvetype element in the final stages of the discharge, near the cut-otr point of the valve-type element, and said series gap-means being capable of interrupting the combined currents of both said valve-type element and said resistor at the rated voltage of the protective device.

3. An excess-voltage protective device comprising' a. variable-resistance valve-type element capable of passing heavy discharge-currents when impressed with voltages in excess o! the rated voltage of the protective device, and f substantially interrupting said discharge upon the return of rated voltage-conditions, a resistor ot relatively fixed resistance, a main series gapmeans in series with the valve-type element. an auxiiiary series gap-means in series with the resistor, and means for connecting said reslsto and said auxiliary Gap-means in shunt to said valve-type element and in series with said main gap-means.

. WILLIAM E. BERKEY.

F EDERICK B JOHNSON. 

